We’ve shared a good bit about the seemingly odd senses dogs possess. They can’t talk to us in the same way we talk to each other, but they are highly attentive animals that learn to pick up on a multitude of nonverbal cues. They seem to know when we’re happy, angry, sad, and any other range of emotions — sometimes even mimicking our moods with their own behavior.
Dogs also have a knack for picking up our changing physical state and not just our emotional state, like actually getting sick. How do they do this? Well, one recent study, for example, revealed that humans create a specific odor during an epileptic seizure and a dog’s sense of smell is so strong and specific that it can detect and recognize this scent, effectively identifying when a person has had an epileptic seizure just by sniffing the sweat secreted during one.
“Dogs are preternaturally sensitive to changes in their people,” says Alexandra Horowitz, the head of the Horowitz Dog Cognition Lab at Barnard College. “If a person is infected with a virus or bacteria, they will smell different.”
Apparently this ability to smell illness isn't exclusive to dogs, as people are capable of the same. However, our olfactory senses aren’t nearly as strong, as plentiful, or able to pinpoint the differences in odors with the same precision dogs have. "Let's suppose they're just 10,000 times better," James Walker, former director of the Sensory Research Institute at Florida State University says about canines having 10,000 to 100,000-times as acute a sense of smell
More research suggests that our changing mood, another thing dogs will recognize intuitively, triggers their sense of smell to confirm something is wrong. Our emotions can manifest in physical changes known as chemical signals the human body gives off, often through sweat, through which people can interact — the exact process studied recently with dogs sensing epileptic seizures. So while people can sense and smell when another human is sick, the scent only needs to be a fraction as strong for a dog to recognize the change and identify it.
Our voice also offers more triggers for our pooches to pick up on. A 2014 study described how dogs possess an area of the brain similar to humans in which they’re enabled the ability to decipher voice tones and associate them with emotions. Humans use this area of the brain not for deciphering language and vocabulary, but for picking apart all the information packed into sounds, like recognizing who is speaking, cues into how they may be feeling, and the intention behind their words. What researchers found in 2014 through brain scans is that neurons in a similar region of a dog’s brain will light up strongly when they hear voices they recognize in their own species barking growling and whining.
"When you looked at how dogs respond to emotional cues in sounds, it's very similar to how humans respond," Andics says. "It's in the same brain region ... and is stronger with positive vocalizations than negative ones…Like people, dogs use simple acoustic parameters to extract out the feelings from a sound," said Attila Andics, a neurobiologist at the MTA-ELTE Comparative Ethology Research Group in Budapest, who led the study. "For instance, when you laugh, 'Ha ha ha,' it has short, quick pieces. But if you make the pieces longer, 'Haaaa, haaaa, haaaa,' it starts to sound like crying or whining. This is what people — and dogs — pay attention to."
This does a lot to explain why dogs perk up when the pitch in our voice goes up while talking to them as if we’re excitedly talking to a newborn. They understand we’re happy in that moment, similar to how they start to recognize the slightest change in our voice when we’re not feeling our 100 percent best at the first hint of the flu.
“We’re sending out lots of cues, of just the sort that dogs are specialized in attuning to,” says Horowitz. “Whether they think that it means ‘sickness’ is not clear,” explaining that in this context, dogs’ senses pique their intrigue. We may think this is them knowing and understanding that we’re sick but according to Horowitz, it’s more that they just seem to know something is “off” and therefore tend to stick a little closer by our side as a way of investigating the unexplainable change in our behavior. This is where their “concern might be vigilance,” says Horowitz, as they suddenly and noticeably become our guard dog. They carry out this role by staying closer to us physically and rarely, if ever, leaving us alone.
So it’s actually a collection of senses that lead a dog to be our comfort and support animals when we’re not feeling our best, another big plus in the man’s best friend column.